Growth and physiological responses of two phenotypically distinct accessions of centipedegrass (Eremochloa ophiuroides (Munro) Hack.) to salt stress

Enhancing stimulation of cyaniding, GhLDOX3 activates reactive oxygen species to regulate tolerance of alkalinity negatively in cotton

Anthocyanins belong to flavonoid secondary metabolites that act as plant pigments to give flowers and fruits different colors and as "scavengers" of reactive oxygen species (ROS) to protect plants from abiotic and biotic stresses. Few studies linked anthocyanins to alkaline resistance so far. In this study, anthocyanin synthesis-related gene leucoanthocyanidin dioxygenase (LDOX) was screened as a candidate gene to explore its relationship with alkali stress. The results found that pYL156: GhLDOX3 lines treated with 50 mM Na2CO3 (pH 11.11) for 24 h showed a significant increase in peroxidase (POD) activity, a decrease in total anthocyanin content and an increase in cyanidin content and a decrease in ROS accumulation compared to pYL156. The overexpressed (OE) lines, ldox mutant and wild-type (WT) lines in Arabidopsis were treated with 50 mM Na2CO3, 100 mM Na2CO3 and 150 mM Na2CO3 for 8 d, respectively. The wilted degree of the OE lines was more severe than WT lines, and less severe in the mutant lines in the 150 mM Na2CO3 treatment. After treatment, the expression levels of AtCAT and AtGSH genes related to antioxidant system in OE lines were significantly lower than in WT, and the expression levels of AtCAT and AtGSH in mutant lines were significantly higher than in WT. In conclusion, the above results suggest GhLDOX3 played a negative regulatory role in the mechanism of resisting Na2CO3 stress. Therefore, it can be considered in cotton breeding to improve the alkali tolerance of cotton by regulating the expression of related genes.

The Role of Anthocyanins in Plant Tolerance to Drought and Salt Stresses

Drought and salinity affect various biochemical and physiological processes in plants, inhibit plant growth, and significantly reduce productivity. The anthocyanin biosynthesis system represents one of the plant stress-tolerance mechanisms, activated by surplus reactive oxygen species. Anthocyanins act as ROS scavengers, protecting plants from oxidative damage and enhancing their sustainability. In this review, we focus on molecular and biochemical mechanisms underlying the role of anthocyanins in acquired tolerance to drought and salt stresses. Also, we discuss the role of abscisic acid and the abscisic-acid-miRNA156 regulatory node in the regulation of drought-induced anthocyanin production. Additionally, we summarise the available knowledge on transcription factors involved in anthocyanin biosynthesis and development of salt and drought tolerance. Finally, we discuss recent progress in the application of modern gene manipulation technologies in the development of anthocyanin-enriched plants with enhanced tolerance to drought and salt stresses.

Comparative Analysis of Antioxidant System and Salt-Stress Tolerance in Two Hibiscus Cultivars Exposed to NaCl Toxicity

Hibiscus (Hibiscus syriacus L.) is known as a horticultural plant of great ornamental and medicinal value. However, the effect of NaCl stress on hibiscus seedlings is unclear. Little is known about H. syriacus 'Duede Brabaul' (DB) and H. syriacus 'Blueberry Smoothie' (BS). Here, the effects of solutions with different concentrations of NaCl on the organic osmolytes, ion accumulation, and antioxidant enzyme activity of hibiscus seedling leaves were determined. The results showed that the Na⁺/K⁺ ratio was imbalanced with increasing NaCl concentration, especially in BS (range 34% to 121%), which was more sensitive than DB (range 32% to 187%) under NaCl concentrations of 50 to 200 mM. To cope with the osmotic stress, the content of organic osmolytes increased significantly. Additionally, NaCl stress caused a large increase in O₂·^- and H₂O₂, and other reactive oxygen species (ROS), and antioxidant enzyme activity was significantly increased to remove excess ROS. The expression level of genes related to salt tolerance was significantly higher in DB than that in BS under different NaCl concentrations. Taken together, DB possessed a stronger tolerance to salt stress and the results suggest membrane stability, Na⁺/K⁺, H₂O₂, catalase and ascorbate peroxidase as salt tolerance biomarkers that can be used for gene transformation and breeding in future hibiscus research.

A turn-on NIR fluorescent probe for risk-assessing oxidative stress in cabbage roots under abiotic stress

Oxidative stress is closely related to the crop health status under stress conditions. H₂O₂ is an important signaling molecule in plants under stress. Therefore, monitoring H₂O₂ fluctuations is of great significance when risk-assessing oxidative stress. However, few fluorescent probes have been reported for the in situ tracking of H₂O₂ fluctuations in crops. Herein, we designed a "turn-on" NIR fluorescent probe (DRP-B) to detect and in situ-image H₂O₂ in living cells and crops. DRP-B exhibited good detection performance for H₂O₂ and could image endogenous H₂O₂ in living cells. More importantly, it could semi-quantitatively visualize H₂O₂ in cabbage roots under abiotic stress. Visualization of H₂O₂ in cabbage roots revealed H₂O₂ upregulation in response to adverse environments (metals, flood, and drought). This study provides a new method for risk-assessing oxidative stress in plants under abiotic stress and is expected to provide guidance for the development of new antioxidant defense strategies to enhance plant resistance and crop productivity.

Turfgrass Salinity Stress and Tolerance-A Review

Turfgrasses are ground cover plants with intensive fibrous roots to encounter different edaphic stresses. The major edaphic stressors of turfgrasses often include soil salinity, drought, flooding, acidity, soil compaction by heavy traffic, unbalanced soil nutrients, heavy metals, and soil pollutants, as well as many other unfavorable soil conditions. The stressors are the results of either naturally occurring soil limitations or anthropogenic activities. Under any of these stressful conditions, turfgrass quality will be reduced along with the loss of economic values and ability to perform its recreational and functional purposes. Amongst edaphic stresses, soil salinity is one of the major stressors as it is highly connected with drought and heat stresses of turfgrasses. Four major salinity sources are naturally occurring in soils: recycled water as the irrigation, regular fertilization, and air-borne saline particle depositions. Although there are only a few dozen grass species from the Poaceae family used as turfgrasses, these turfgrasses vary from salinity-intolerant to halophytes interspecifically and intraspecifically. Enhancement of turfgrass salinity tolerance has been a very active research and practical area as well in the past several decades. This review attempts to target new developments of turfgrasses in those soil salinity stresses mentioned above and provides insight for more promising turfgrasses in the future with improved salinity tolerances to meet future turfgrass requirements.

Comparative study on growth traits and ions regulation of zoysiagrasses under varied salinity treatments

Salt stress affects plant physiology, development, and growth. This research investigated varied salinity levels on growth traits and ions accumulation of four zoysiagrasses and aimed to identify phenotypic traits associated with variability in salinity tolerance. In this study, “S001” zoysiagrass (Zoysia sinica), “Diamond” zoysiagrass (Zoysia matrella), “J026” zoysiagrass (Zoysia japonica), and “M001” zoysiagrass (Zoysia macrostachya) were grown in plastic pots and exposed to 1/2 Hoagland nutrient solution amended with different amounts of NaCl for 120 days. At the end of the experiment, growth traits and ion contents were determined. The results showed that the salt-tolerance of four zoysiagrasses ranked as “M001” > “Diamond” > “J026” > “S001” according to percent green leaf canopy area (GLCA) after 120 days of salinity treatment. Although dry leaf weight, leaf length/width, and shoot height were significantly decreased by salinity treatments for all turfgrasses, the salt-tolerant species had a smaller drop. Besides, ions secretion capacity and Na⁺ concentration in leaf and root increased, but K⁺ concentration together with leaf and root K⁺/Na⁺ ratios decreased with the increasing concentration of the salinity. However, the salt-tolerant species exhibited strong K⁺ absorption and transportation ability and a high salt secretion capacity. The results indicated that growth traits and ions regulation were related to variability in tolerance of diverse zoysiagrasses to salt stress.

Physiological responses and tolerance mechanisms of seashore paspalum and centipedegrass exposed to osmotic and iso-osmotic salt stresses

Osmotic stresses caused by reduced water availability or the accumulation of salts in the soil can be highly damaging to plants. The objective of this study was to investigate physiological responses and tolerance mechanisms of two turfgrass species (seashore paspalum and centipedegrass) with distinct differences in salinity tolerance exposed to osmotic and iso-osmotic salt stresses. Three turfgrass genotypes including seashore paspalums 'Seastar' and 'UGP113', and centipedegrass 'TifBlair' were grown in ½ strength Hoagland's solution with three different treatment conditions; control (no external addition), salt stress (-0.4 MPa by adding NaCl) and osmotic stress [-0.4 MPa by adding polyethylene glycol (PEG)]. Osmotic stress damages were more severe with greater reductions in turf quality, photochemical efficiency (Fv/Fm), relative water content (RWC) and leaf water potential (Ψw) compared to iso-osmotic salt stress in both seashore paspalum and centipedegrass. Greater osmotic adjustment (OA) with greater accumulation of metabolically inexpensive inorganic osmolytes (Na⁺) helped turfgrasses to lessen damages in salt stress compared to osmotic stress. However, such accumulation of Na⁺ resulted ion-toxicity and triggered some damages in terms of increased electrolyte leakage (EL) and reduced total protein in salt-sensitive centipedegrass. Seashore paspalum had better ion regulation and also maintained greater antioxidant enzyme activities compared to centipedegrass; therefore it was able to avoid ion-specific damages under salt stress. Differences in the utilization of specific solutes for osmotic adjustment and antioxidant metabolism are partially responsible for the differences in salt versus osmotic stress responses in these species; the regulation of these defense mechanisms requires further investigation.

Hydrogen sulfide mediated alleviation of cadmium toxicity in Phlox paniculata L. and establishment of a comprehensive evaluation model for corresponding strategy

A laboratory experiment was performed to evaluate the potential role of H₂S on cadmium (Cd) toxicity in Phlox paniculata L. Seeds pretreated with 0.3, 0.6, 0.9, and 1.2 mM NaHS as a donor of H₂S for 24 h and subsequently exposed to 100, 200, and 300 μM CdCl₂ for 26 days had significantly higher germination rate compared with Cd alone. Meanwhile, 2-year-old seedlings sprayed with 0.3, 0.6, and 0.9 μM NaHS were grown in soil with 0.3, 0.6, and 1.2 mg/kg CdCl₂, respectively. We observed that H₂S decreased Cd accumulation in leaves and elevated Cd concentration in roots. Cd toxicity in seedlings resulted in a substantial increase in Cd-induced overproduction of malondialdehyde (MDA), Cd accumulation, and electrolyte leakage. Meanwhile, addition of NaHS increased photosynthetic performance compared with Cd alone. Exogenous H₂S significantly elevated biomass, improved antioxidant enzyme activities, and reduced ABA content compared with Cd alone. H₂S also plays an important role in the ABA signaling pathway during stress. Notably, NaHS promoted Cd uptake by Phlox paniculate L. from soil. The prediction model of H₂S for increasing plant resistance and reducing soil Cd pollution was established by factor analysis method based on comprehensive evaluation of plant stress physiology.

Genetic diversity in centipedegrass [Eremochloa ophiuroides (Munro) Hack.]

Genetic diversity is the heritable variation within and among populations, and in the context of this paper describes the heritable variation among the germplasm resources of centipedegrass. Centipedegrass is an important warm-season perennial C4 grass belonging to the Poaceae family in the subfamily Panicoideae and genus Eremochloa. It is the only species cultivated for turf among the eight species in Eremochloa. The center of origin for this species is southern to central China. Although centipedegrass is an excellent lawn grass and is most widely used in the southeastern United States, China has the largest reserve of centipedegrass germplasm in the world. Presently, the gene bank in China holds ~200 centipedegrass accessions collected from geographical regions that are diverse in terms of climate and elevation. This collection appears to have broad variability with regard to morphological and physiological characteristics. To efficiently develop new centipedegrass varieties and improve cultivated species by fully utilizing this variability, multiple approaches have been implemented in recent years to detect the extent of variation and to unravel the patterns of genetic diversity among centipedegrass collections. In this review, we briefly summarize research progress in investigating the diversity of centipedegrass using morphological, physiological, cytological, and molecular biological approaches, and present the current status of genomic studies in centipedegrass. Perspectives on future research on genetics and genomics and modern breeding of centipedegrass are also discussed.

Physiological and Transcriptional Responses of Industrial Rapeseed (Brassica napus) Seedlings to Drought and Salinity Stress

Abiotic stress greatly inhibits crop growth and reduces yields. However, little is known about the transcriptomic changes that occur in the industrial oilseed crop, rapeseed (Brassica napus), in response to abiotic stress. In this study, we examined the physiological and transcriptional responses of rapeseed to drought (simulated by treatment with 15% (w/v) polyethylene glycol (PEG) 6000) and salinity (150 mM NaCl) stress. Proline contents in young seedlings greatly increased under both conditions after 3 h of treatment, whereas the levels of antioxidant enzymes remained unchanged. We assembled transcripts from the leaves and roots of rapeseed and performed BLASTN searches against the rapeseed genome database for the first time. Gene ontology analysis indicated that DEGs involved in catalytic activity, metabolic process, and response to stimulus were highly enriched. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that differentially expressed genes (DEGs) from the categories metabolic pathways and biosynthesis of secondary metabolites were highly enriched. We determined that myeloblastosis (MYB), NAM/ATAF1-2/CUC2 (NAC), and APETALA2/ethylene-responsive element binding proteins (AP2-EREBP) transcription factors function as major switches that control downstream gene expression and that proline plays a role under short-term abiotic stress treatment due to increased expression of synthesis and decreased expression of degradation. Furthermore, many common genes function in the response to both types of stress in this rapeseed.

Functional and genomic characterization of a wound- and methyl jasmonate-inducible chalcone isomerase in Eremochloa ophiuroides [Munro] Hack

Eremochloa ophiuroides, a perennial warm-season lawn grass, has a characteristic phenotype of red pigmentation in tissues during maturation. The putative gene families associated with the red coloration were previously identified in E. ophiuroides. These genes encode chalcone synthases, flavonol 3-hydroxylases, and flavonol 3'-hydroxylases, acting on the early flavonoid-biosynthesis pathway. Here, a type-I chalcone isomerase (CHI) gene was isolated from E. ophiuroides based on leaf-transcriptome data, and the corresponding enzyme was functionally characterized in vitro and in planta. Complementation of Arabidopsis tt5 mutants by overexpressing EoCHI recapitulated the wild-type seed coat color. Wounding and methyl jasmonate treatments significantly elevated the transcript level of EoCHI and total anthocyanin content in shoots. Confocal microscopy indicated the localization of EoCHI to the endoplasmic reticulum. The genomic EoCHI sequence contained two introns with a novel pattern of exon‒intron organization. Further examinations on genomic structures of CHI family from ancient to advanced plant lineages should be of interests to decipher evolutionary pathways of extant plant CHI genes.

De novo assembly and comparative transcriptome analysis reveals genes potentially involved in tissue-color changes in centipedegrass (Eremochloa ophiuroides [Munro] Hack.)

Turf color is the most important characteristics of visual quality for a turfgrass species with high ornamental value and wide application prospects. Centipedegrass is a well-adapted warm-season turfgrass species in tropical, subtropical and temperate regions, possessing many outstanding properties including uniform green color. However, quite a few centipedegrass accessions or cultivars produce stolons and spike tissues with red-purple color, thereby decreasing their aesthetic value. A research focus in centipedegrass is to develop high-quality cultivars with uniform green color. To explore the major genes associated with the color changes in certain organs/tissues contributes to understand the molecular mechanisms of the same tissues having different phenotypic characteristics. In the present study, two phenotypically distinct centipedegrass accessions, E092 being a wild-type (WT) with red-purple stolons and spike tissues and E092-1 being a mutant (MT) with uniform green stolons and spike tissues, were used. Using the Illumina sequencing platform, approximately 401.7 million high-quality paired-end reads were obtained. After de novo assembly and quantitative assessment, 352,513 transcript sequences corresponding to 293,033 unigenes were generated with an average length of 735 bp. A total of 145,032 (49.49%) unigenes were annotated by alignment with public protein databases. Of these unigenes, 329 differentially expressed genes (DEGs) were identified between WT and MT stolons, with 156 up-regulated and 173 down-regulated; and 829 DEGs were detected between WT and MT spike tissues, including 497 up-regulated and 332 down-regulated. The expression profile of 10 randomly selected DEGs was confirmed with RT-qPCR. Candidate genes involved in the flavonoid biosynthesis were identified showing significant transcript changes between WT and MT organs/tissues. And transcript abundances of these flavonoid biosynthetic pathway-related genes were positively correlated with the accumulation of total anthocyanin in respective organs/tissues. This assembled transcriptome of centipedegrass can be served as a global description of expressed genes of above-ground organs/tissues and provide more molecular resources for future functional characterization analysis of genomics in warm-season turfgrass. Identified genes related to centipedegrass organ/tissue changes will contribute to molecular improvement of turf quality through genetic manipulation.